Recent evidence indicates that cells within a tumor are heterogeneous and represent different stages of development (Clarke et al. 2006. Cancer Res. 66:9339-9344). In certain types of cancer, a population of cells has been identified that are termed cancer stem cells, where a cancer stem cell is defined as a cell that has the capacity to self-renew and to cause the heterogeneous lineages of cancer cells that comprise a tumor. Experimentally, such cells are ones that have the ability to generate a continuously growing tumor (Clarke et al. 2006. Cancer Res. 66:9339-9344). Cancer stem cells can arise from normal stem cells but also from cells that acquire the capacity to self-renew potentially due to a series of mutagenic events within the cell. There is considerable interest in the role of cancer stem cells in certain types of cancer. Cancer types that have been associated with the presence of cancer stem cells include breast cancer (Al-Hajj et al. 2003. PNAS 100:3983-3988), pancreatic cancer (Hermann et al. 2007. Cell Stem Cell 1:313-323), brain cancer (Singh et al. 2004. Nature 432:396-401), and testicular cancer (Houldsworth et al. 2006. J. Clin. Oncol. 24:5512-5518; Clark A. T. 2007. Stem Cell Rev. 3:49-59.
Testicular germ cell tumors (TGCTs), the most common solid tumors of adolescent and young men, are thought to derive from transformation of primordial germ cells (PGCs) or early gonocytes (Houldsworth et al. 2006. J. Clin. Oncol. 24:5512-5518; Clark A. T. 2007. Stem Cell Rev. 3:49-59). TGCTs are classified as seminomas and nonseminomas (Houldsworth et al. 2006. J. Clin. Oncol. 24:5512-5518). Within nonseminomas are undifferentiated, pluripotent cells, known as embryonal carcinoma (EC) cells. EC cells are proposed to represent the stem cells of TGCTs and to be the malignant counterparts to embryonic stem (ES) cells (Houldsworth et al. 2006. J. Clin. Oncol. 24:5512-5518; Clark A. T. 2007. Stem Cell Rev. 3:49-59). EC cells can differentiate in vivo toward extra-embryonic tissues and embryonic tissues.
Patients with TGCTs, even those with advanced metastatic disease, are successfully treated with cisplatin-based chemotherapeutic regimens (Giuliano et al. 2006. Curr. Cancer Ther. Rev. 2:255-270; Einhorn, L. H. 2002. Proc. Natl. Acad. Sci. USA 99:4592-4595). However, 15-20% of patients are refractory to treatment and succumb to progressive disease (El-Helw, L. and R. E. Coleman. 2005. Cancer Treat. Rev. 31:197-209). Some germ cell tumor patients who initially respond to treatment can exhibit a late relapse and have a poor prognosis (Giuliano et al. 2006. Curr. Cancer Ther. Rev. 2:255-270; El-Helw, L. and R. E. Coleman. 2005. Cancer Treat. Rev. 31:197-209). Additionally, testicular cancer survivors have increased incidence of infertility, cardiovascular disease and secondary malignancies (Chaudhary et al. 2003. Drugs 63:1565-1577), all of which can affect ultimate survival and quality of life of testicular cancer patients. Mouse models of testicular cancer do exist, but they do no recapitulate key features of the human malignancy (Houldsworth et al. 2006. J. Clin. Oncol. 24:5512-5518).
Mechanisms of inherent or acquired cisplatin resistance in other tumors have not yet provided insights into the exquisite cisplatin-sensitivity of TGCTs (Giuliano et al. 2006. Curr. Cancer Ther. Rev. 2:255-270). That patients with advanced stage TGCTs can be cured implies that the stem cells of TGCTs are effectively targeted with cisplatin-based chemotherapy (Houldsworth et al. 2006. J. Clin. Oncol. 24:5512-5518; Giuliano et al. 2006. Curr. Cancer Ther. Rev. 2:255-270). There is a need to identify other chemotherapeutic agents for use in the patients that do not respond to cisplatin therapy, or that have become resistant to cisplatin therapy.
DNA methylation inhibitors, another class of chemotherapeutic agents, have been found to be more active in leukemia than in solid tumor cells (Qin et al. 2009. Blood 113:659-667). One such drug, 5-aza-deoxycytidine, also known as decitabine, has been shown to be useful for treating leukemia (e.g., Garcia-Manero, G. 2008. Curr. Opin. Oncol. 20:705-710). Decitabine is currently approved in the United States for the treatment of myelodysplastic syndromes which include leukemia. Although many papers describe the efficacy of decitabine in the treatment of leukemia, the published medical literature does not support the use of decitabine in the treatment of other types of cancer. For example, Abele et al. (1987. Eur. J. Cancer Clin. Oncol. 23:1921-1924) described the use of decitabine at a dose of 75 mg/m2 (3 treatments in one day; repeated once a week for 5 weeks) for treatment of colorectal cancer, cancer of the head and neck, renal carcinoma, or malignant melanoma. The authors reported that decitabine showed no efficacy against any of the forms of cancer. In another study (Clavel et al. 1992. Ann Oncol. 3:399-400), decitabine was tested in a Phase II clinical trial in patients with non-seminiferous testicular cancer (i.e., germ cell testicular cancer). The authors used a decitabine dose of 75 mg/m2 (3 infusions in one day, repeated once a week for 5 weeks; the standard leukemia regimen) and reported that the drug showed “no activity” in these patients.
U.S. Pat. No. 6,613,753 teaches administering the DNA methylation inhibitor decitabine, in combination with an anti-neoplastic agent, to treat cancer. A long list of cancers is disclosed, including testicular cancer. The patent teaches use of decitabine in combination with chemotherapeutic agents that include cisplatin and to treat cisplatin resistance. The patent teaches and claims a preferred dose range for decitabine of 1-20 mg/m2/day. No data are provided showing successful treatment of germ cell testicular cancer with this regimen.